Experimental and first-principles studies of superconductivity in polycrystalline topological semimetal SnTaS$_2$

Superconductivity paired with topologically protected non-trivial electronic band structure has stimulated great research interest, which offers a promising platform to explore novel quantum states like topological superconductors and Majorana fermions. We report superconducting properties and electronic band structure of topological semimetal candidate SnTaS$_2$. Polycrystalline samples of SnTaS$_2$ were prepared via solid-state reaction route following a sealed tube approach. SnTaS$_2$ crystallizes in a centrosymmetric hexagonal structure (space group: $P6_3/mmc$). Ta occupies the trigonal-prismatic position coordinated with S atoms, and Sn accommodates the octahedral site, create alternative layers of TaS$_2$ and Sn. Systematic studies show that SnTaS$_2$ is a type-II superconductor with $T_c\sim$ 2.8 K. The characteristic upper and lower critical fields are found to be $\mu_0H_{c2}(0)$ = 1458 Oe and $\mu_0H_{c1}(0)$ = 45.5 Oe respectively. First-principles calculations demonstrate signatures for nodal line band characteristics protected by the spatial-inversion and time-reversal symmetries, which strongly gapped out by the inclusion of spin-orbit coupling (SOC). Our results suggest superconductivity in topological semimetal SnTaS$_2$ provides an interesting arena to investigate the possibility for 3D topological superconductivity.